One reason a person or store might say "happy holidays" is because December is a season of holidays for mainstream faiths as well as lesser-knowns. The multi-faith Web site beliefnet.org tracks dozens of religions and publishes news, features and explanatory articles about them. It is the source for the following calendar. (source of this article)
Beginning of Advent (Christian) : Start of a four-week preparation for the coming of Jesus.
Catholic Feast of the Immaculate Conception (Christian) : Commemoration of Mary's conception.
Bodhi Day/Rohatsu (Zen Buddhist) : Commemoration of the Buddha's enlightenment.
Hanukkah (Jewish) : Eight-day festival of lights beginning on the 25th of Kislev commemorating the rededication of the Temple in Jerusalem after its desecration by Syrian King Antiochus in 165 B.C. (begins at sundown the night before).
Mother Night (Heathen) : Eve of Winter Solstice and the holiest night of the year; marks the beginning of the 12 days of Yule.
Winter Solstice/Saturnalia/Yule (Pagan/Wiccan and Heathen) : Pagan observance of the longest night of the year, celebrating the rebirth of the sun god. The first of 12 days of Yule celebrating the Holy Tide of Heathen ancestral ways, community, gift giving and the rebirth of longer days.
Pancha Ganapati (Hindu) : Five-day festival honoring Ganesh, the deity who removes obstacles.
Christmas (Christian) : Celebrates the birth of Jesus Christ.
Zarathosht Diso (Zoroastrian) : Commemoration of the death of the Prophet Zarathustra, a prophet believed to have been from modern-day Iran.
Dec. 26-Jan. 1
Kwanzaa (Interfaith) : Seven-day African-American and Pan-African holiday celebrating family, community and culture.
Hajj (Muslim) : Islamic pilgrimage to Mecca.
Eid al-Adha (Muslim) : Festival of the Sacrifice, a commemoration of Abraham.